1. Field of the Invention
The present invention relates to a file control device handling access requests for file resources when a plurality of access sources in a use systems and a shared system simultaneously use file resources in a network system composed of the shared system and a plurality of use systems.
2. Description of the Related Art
A network system comprises a plurality of shared systems and a plurality of use systems, and these systems are connected to one another by communicable network resources, such as an LAN (local area network) and the like. Each of the shared systems publishes the resources, such as files, etc., of the system to other systems, and each of the use systems performs necessary processes using the resources published by the shared systems.
Each use system comprises applications and a client, and each shared system comprises shared files and a server. An application is a program generated by a user in order to do a job, and a client is a program called up by the application when the application uses the shared file. A shared file is published to the use systems by a shared system, and a server is a program called up by the client when the client uses the shared file.
When in a conventional network system, a plurality of applications use the same shared file, each application refers/updates the file after requesting exclusion. File exclusion by a specific application means that the application obtains a right to exclusively use the file.
However, in the network system described above, all the OSs (operating systems) of a plurality of use systems are not always the same. Sometimes, some systems adopt UNIX (™) and other systems adopt WINDOWS (™). Due to such a difference in platform, sometimes a UNIX (™) application requests exclusion, but a WINDOWS (™) application requests no exclusion.
In the same use system too, sometimes an application requesting exclusion and an application requesting no exclusion co-exist. Furthermore, sometimes, there are applications using a shared file in the shared system. For this reason, if the following conditions are met, data are destroyed.    (1) When a plurality of applications in a use system and a shared system simultaneously perform the update process of one shared file.    (2) When there is an application requesting no exclusion.
In this case, since there is an application requesting no exclusion, leak is caused in exclusion. As a result, the data writing in a file is duplicated by two or more applications and the data are destroyed since unintended data writing is performed.